Embodiments of the invention relate generally to rotary electric machines and, more particularly, to a rotary electric machine with plural rotary elements in a non-coaxial arrangement.
Electric machines that function as motors and generators have been known in the art for many years. Electric motors range in size and output and operation. Electric motors use electric current or voltage as an input and then output rotation to a shaft member. Conversely, electric generators/alternators receive the rotation of a shaft as input and then output an electric current or voltage. The application of electric machines is widely varied and can be applied in industrial applications for differential drive of adjacent machine sections or can be applied in a vehicle electric drive platform as part of an electric or hybrid vehicle, for example.
Certain electric machines have been developed that utilize multiple rotors and/or multiple stators, and various designs that relate to construction and control of electric machines having multiple coaxial rotors that are not mechanically coupled have been previously set forth. Such machines can generally be divided into two design categories: (1) a radial layer design in which the rotors are concentrically sandwiched; (2) a side-by-side design in which the rotors are axially adjacent. Most of the early multi-rotor electric machines were DC machines of the radial layer design, and the earliest had counter-rotating rotors with armature windings mounted on one rotor and field windings mounted on the other rotor, such as set forth in U.S. Pat. Nos. 424,818, 1,348,539, 2,462,182 and 3,308,318. An early example of a machine with coaxial side-by-side rotors is given in U.S. Pat. No. 1,858,506.
With respect to the use of electric machines in a vehicular application, the trends in automotive technology point in the direction of plug-in extended-range electric vehicles with series hybrid power trains. As a result, there is considerable current interest in multi-rotor electric machines with differential torque/speed and electric regeneration capabilities. In U.S. Pat. No. 5,172,784, a hybrid electric propulsion system is disclosed that includes a motor having synchronized rotors aligned by a central pilot bearing. U.S. Pat. No. 5,793,136 discloses a differential motor/generator of the radial layer design in which two rotors interact mutually with shared stator windings. Additional, several patents disclose motor/generators having sandwiched or coaxial side-by-side rotors, such as U.S. Pat. No. 6,049,152 which describes rotors having different numbers of magnetic poles, and an electronic control supplying composite stator current which allows the rotors to operate at different synchronous speeds.
The use of multiple coaxial rotors is set forth in U.S. Pat. No. 6,297,575, which describes an electric machine having a three layer structure “sharing a common axis” with “two independently interactive coaxial electromechanical effect actuators,” and in U.S. Pat. No. 6,373,160, which sets forth an electric machine that includes an electronic motor control and “separate rotors . . . having a same axis of rotation,” and in U.S. Pat. No. 6,922,004, which discloses an axial flux motor assembly with coaxial side-by-side rotors having planetary output gearing. In the October 2008 issue of Sadhana, a journal of the Indian Academy of Sciences, a paper presents the construction and equivalent electric circuit of a differential induction machine with coaxial side-by-side rotors.
The paradigm in all of the aforementioned inventions is that the rotors are coaxial. While the use of coaxial rotors is necessary in a radial layer design, such an arrangement is not needed in a side-by-side design. While functional, the prior design of electric machines to have rotors in a coaxial, side-by-side arrangement presents limitations on the design of the electric machine. For example, arranging the rotors in a coaxial arrangement may be undesirable when incorporating the machine into an electric or hybrid vehicle where the amount of space may be limited.
Therefore, it would be desirable to design a rotary electric machine with plural rotary elements not subject to unnecessary coaxial restriction, in order to provide a space saving arrangement. It would further be desirable for the rotary electric machine to provide for rotation of the plural rotary elements at differential speeds, such that the rotary electric machine can be implemented in a vehicle electric drive platform or other system in which differential speeds are desired.